Near 100% spectral-purity photons from reconfigurable micro-rings**Project supported by the National Basic Research Program of China (Grant Nos. 2017YFA0303700 and 2019YFA0308700), the National Natural Science Foundation of China (Grant Nos. 61632021 and 11690031), and the Open Funds from the State Key Laboratory of High Performance Computing of China (HPCL, National University of Defense Technology).

Abstract

We propose an on-chip reconfigurable micro-ring to engineer the spectral-purity of photons. The micro-ring resonator is designed to be coupled by one or two asymmetric Mach–Zehnder interferometers and the coupling coefficients hence the quality-factors of the pump and the converted photons can be dynamically changed by the interferometer’s internal phase-shifter. We calculate the joint-spectrum function and obtain the spectral-purity of photons and Schmidt number under different phases. We show that it is a dynamical method to adjust the spectral-purity and can optimize the spectral-purity of photons up to near 100%. The condition for high-spectral-purity photons is ensured by the micro-ring itself, so it overcomes the trade-off between spectral purity and brightness in the traditional post-filtering method. This scheme is robust to fabrication variations and can be successfully applied in different fabrication labs and different materials. Such high-spectral-purity photons will be beneficial for quantum information processing like Boson sampling and other quantum algorithms.